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Reviewed research
Authors Eisenberg ML, Kim S, Chen Z, et al.
Review Date January 2014
Citation Human Reproduction 2014; 29(2 ): 193–200.
Background
Higher body mass index (BMI) has been shown to be associated with impaired semen parameters, although not in all studies, and some studies have shown improvement in semen parameters with weight loss. However, waist circumference (WC), a measure of body fat distribution, has not been as well studied with respect to semen parameters and so far only assessed in infertile men. The effect of physical activity on fertility is uncertain.
Aim
The authors aimed to explore the separate and combined effects of BMI, WC and physical activity on semen parameters among male partners of couples attempting to become pregnant from a population sample.
Methods
The Longitudinal Investigation of Fertility and the Environment (LIFE) study is a population-based prospective cohort of 501 couples attempting to conceive, from two geographical areas in the USA, recruited in 2005-2009. Couples were recruited from four counties in Michigan and 12 counties in Texas to ensure a range of environmental exposures and lifestyle characteristics. In person interviews were conducted to ascertain demographic, health and reproductive histories followed by anthropometric assessment. Semen samples were obtained from 468 men (93%) of whom 378 provided two samples.
BMI (kg/m2) was categorised as < 25.0 (underweight and normal), 25.0–29.9 (overweight) 30.0–34.9 (obese, class I) and ≥ 35 (obese, class II) for analysis. Data were available for analysis in 468 men (93%),
Results
Participants had a mean +/- SD age of 31.8 +/- 4.8 years, BMI of 29.8 +/- 5.6 kg/m2 and WC of 100.8 +/- 14.2 cm. Most men were either overweight (41%) or obese (41%); 58% reported physical activity < 1 time/week. 53% had never fathered a child.
The median sperm concentration for the men in the cohort was 60.2 M/ml with 8.6% having oligospermia (< 15 M/ml). When examining semen parameters, ejaculate volume showed a linear decline with increasing BMI and WC(P < 0.01). Similarly, the total sperm count showed a negative linear association with WC (P< 0.01). No significant relationship was seen between either BMI or WC and semen concentration, motility, vitality, morphology or DNA fragmentation index.
The percentage of men with abnormal volume, concentration and total sperm increased with increasing BMI and increasing WC, although the evidence for the association between WC and low volume was weak (p=0.099). No relationship between physical activity and semen parameters was identified.
Conclusion
Participants had a mean +/- SD age of 31.8 +/- 4.8 years, BMI of 29.8 +/- 5.6 kg/m2 and WC of 100.8 +/- 14.2 cm. Most men were either overweight (41%) or obese (41%); 58% reported physical activity < 1 time/week. 53% had never fathered a child.
The median sperm concentration for the men in the cohort was 60.2 M/ml with 8.6% having oligospermia (< 15 M/ml). When examining semen parameters, ejaculate volume showed a linear decline with increasing BMI and WC(P < 0.01). Similarly, the total sperm count showed a negative linear association with WC (P< 0.01). No significant relationship was seen between either BMI or WC and semen concentration, motility, vitality, morphology or DNA fragmentation index.
The percentage of men with abnormal volume, concentration and total sperm increased with increasing BMI and increasing WC, although the evidence for the association between WC and low volume was weak (p=0.099). No relationship between physical activity and semen parameters was identified.
Points to Note
There were some important limitations to the study:
- The cohort had a high proportion of overweight and sedentary men, limiting generalisability of the findings.
- The physical activity measure was crude, less than one versus one or more episodes of vigorous activity per week, making it difficult to interpret the physical activity associations (or lack thereof).
- Semen parameters are not very accurate measures of fertility and the study did not include pregnancy success rates for the cohort so it is unclear how the findings relate to infertility per se.
- Despite the limitations, the negative linear associations exhibited between body mass index and waist circumference and serum parameters suggests further research is warranted to examine impacts on fertility.
- Following from these kinds of observational studies there is a need to examine the effect of weight loss on serum parameters and fertility and ways to manage obese men with infertility.
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